Tone-
Beg to differ on the UK definitions:
Vmax: highest IAS achievable in level flight at maximum power/torque.
Vno: Vne - 10 (%?) UK idea is that this gives a sensible buffer to avoid exceedence of Vne.
Vne: max permitted certificated IAS.
Vdf: max possible IAS before 'orrible things likely to 'appen (but flown to during certification process: that's what prototypes are for!)